In 2008 the excavation for a house site at Westmere/Rapanui uncovered a 400-year-old burial site which became a headache for the owners and Wanganui District Council.
After fuss and bother that situation was resolved. But it has pushed the council to get more proactive about its historic sites. In 2011 it commissioned research that added 720 new sites, including 87 pa (fortified Maori villages), 178 kainga (Maori villages) and 173 pits.
The council now has more than 1000 sites listed and is sending out letters to inform people who have sites on their properties. It's also asking whether they mind if most of the sites are no longer listed in its District Plan - and the information is stored at council on electronic maps instead.
One of the council's senior policy analysts, Clive Aim, said about 380 letters, each including a map and brief information about each site, had already been sent. There were about 20 more to send, but those had been delayed by uncertainty about site information.
He's had about 15 phone calls since the first lot of letters went out and plans to make some site visits as a result of what he has heard.
It's a lot better to be prepared for the presence of a historic site on your land than to find one by chance, as the builders at Westmere did.
Since the 1993 Historic Places Act historic sites have been defined as places with pre-1900 remains, and landowners are liable if they modify or destroy one.
People considering a development are encouraged to find out from the council whether a heritage site is at risk. If it will be altered, they need authority from the New Zealand Historic Places Trust.
Mr Aim said it was lucky Michael Taylor and Annetta Sutton of Archaeology North moved to Wanganui in the late 1990s. Consulting them was quick and inexpensive
When the Te Taurawhiri pou (pole) had to be buried in Queen's Park, for example, Mr Taylor dug a few preliminary spadefuls and found a piece of slate dating from the days when there was a school there, and some glass from the a redoubt.
The next spadefuls were undisturbed sand, and the rest of the hole could be dug with no problem.
"It only took about five minutes," Mr Aim said.
The proposed alternative to listing sites in the District Plan would be electronic maps at council. They would eventually move online, Mr Aim said.
Putting hundreds more sites into the plan would be time-consuming and expensive, and once they were there it would be time-consuming and expensive to remove or change them.
The most sacred of the sites would be mapped as large areas, with the actual site unidentified. Keeping it vague would prevent people desecrating graves to get greenstone or other valuables. The exact spots would be known only to a few in the relevant iwi (tribe), who could be consulted if necessary.
The council has been gradually increasing its knowledge of heritage sites through site surveying by the New Zealand Archaeological Association and commissioning Archaeology North to examine old documents and aerial photographs.
The sites include pre-1900 European homesteads and industries. The central city and the sides of rivers and lakes are the places where new development is most likely to encroach on historic sites.
Most of the sites identified have never been visited and formally mapped. Mr Aim said that would be done as resources permitted. "We are never going to find everything, but the more we do find, the more we know where we have to be watchful."